I meant to reply to this weeks ago but got behind, my apologies. There was a guest in a ECV most of the time on our voyage - we seemed to find ourselves on similar schedules/in similar circumstances on/off over the trip and from my outsider vantage point it didn't seem to interfere in any material way. I occasionally saw her walking but most of the time was in the ECV, even at the Sabacc table.
ECVs don't fit in the rooms but there are stations/charging areas in a couple of spots along the hallways specifically where ECVs should be parked overnight.